Lens: Nikon M Plan 20x/0.40 210/0 LWD
Vintage: 1990's?
Lens Mount: RMS mount (0.8 in x 36 tpi)
Needed Adapters: This lens has a traditional microscope mounting. I use a RMS to T-mount
adapter and a T-mount to camera-specific adapter.
adapter and a T-mount to camera-specific adapter.
Preferred Mounting: Normal.
Filter Thread: None.
Controls: This lens has no controls.
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Corner Sharpness vs Aperture:
Corner sharpness is good for this lens at all
magnification levels. Not quite as good at 16:1
magnification although the lens is made to work
best at 20:1.
Corner sharpness is good for this lens at all
magnification levels. Not quite as good at 16:1
magnification although the lens is made to work
best at 20:1.
Sharpness and Resolution vs Magnification:
This lens shows only so-so sharpness across its
usable magnification range of about 16:1 to 25:1.
The resolution is quite a lot better, don't let the
relatively low numbers fool you. At 25:1 this lens
is resolving details at a little smaller than 0.7
micrometers, the highest resolution that I have
yet measured for a lens.
The numbers may be artificially a little low as my
test pattern slide is not really made to work at this
magnification (I don't know of one that is at
present). The slant-edge pattern starts to get a
little rough when viewed this up close and
personally.
The reason that this lens can resolve tiny details
is related to its rather large aperture. The
aperture is fixed at about f/1.2. This translates
into a working numerical aperture of 0.40 at 20:1
magnification.
This lens shows only so-so sharpness across its
usable magnification range of about 16:1 to 25:1.
The resolution is quite a lot better, don't let the
relatively low numbers fool you. At 25:1 this lens
is resolving details at a little smaller than 0.7
micrometers, the highest resolution that I have
yet measured for a lens.
The numbers may be artificially a little low as my
test pattern slide is not really made to work at this
magnification (I don't know of one that is at
present). The slant-edge pattern starts to get a
little rough when viewed this up close and
personally.
The reason that this lens can resolve tiny details
is related to its rather large aperture. The
aperture is fixed at about f/1.2. This translates
into a working numerical aperture of 0.40 at 20:1
magnification.
Street Price: ~$200 - $350 in good used condition.
Chromatic Aberration: This lens show mild color fringing in the center
(about 0.80 - 1.6 pixel) and severe on the periphery (9-11 pixels). Anything
below 1.0 pixel is good.
(about 0.80 - 1.6 pixel) and severe on the periphery (9-11 pixels). Anything
below 1.0 pixel is good.
Image Contrast: Image contrast is very good across the magnification range,
typical for microscope objectives.
typical for microscope objectives.
Flare: No significant flare is evident during lens testing.
Conclusion:
This is a microscope objective that works well as a bellows lens. It is sometimes available on eBay for
a fairly reasonable price. It is fairly easy to adapt to a bellows as it has a standard RMS mount.
This lens shows so-so sharpness, but it does show very high resolution capabilities owing to its large
aperture (f/1.2). The resolution comes at the price of almost no depth of field. It required me to stack
128 images to make the sample picture above. Imaging with this lens can be very tedious and
requires special equipment to focus with any precision (I use a microscope stage to focus and keep
the lens and camera stationary). I tend to stick to 10x objectives and lower for most duties.
The lens has good corner sharpness across the magnification range. There is quite a lot of chromatic
aberration present on the periphery of the images. This is not so obvious when the images are
resized down to a sane levels.
The working distance is at the lower limits of utility for imaging with reflected light. It is difficult to get
light on the subject when the front of the lens is between 4 mm and 7mm from the object. A typical 20x
objective will have a working distance of about 3 mm - not enough for good lighting with reflected light.
This LWD (Long Working Distance) objective doubles that. There are 20x objectives out there that
provide even more working distance. These are generally called SLWD (Super LWD) and ELWD
(Extra LWD).
When compared to other lenses in its magnification range, 12 mm bellows lenses, this lens
out-resolves all of them. The only specification that it compares unfavorably with a 12 mm bellows lens
is in the chromatic aberration numbers and the color fringing is not so obvious with real-world image
sizes. They tend to have comparable or minimally better working distance than this objective.
This is a microscope objective that works well as a bellows lens. It is sometimes available on eBay for
a fairly reasonable price. It is fairly easy to adapt to a bellows as it has a standard RMS mount.
This lens shows so-so sharpness, but it does show very high resolution capabilities owing to its large
aperture (f/1.2). The resolution comes at the price of almost no depth of field. It required me to stack
128 images to make the sample picture above. Imaging with this lens can be very tedious and
requires special equipment to focus with any precision (I use a microscope stage to focus and keep
the lens and camera stationary). I tend to stick to 10x objectives and lower for most duties.
The lens has good corner sharpness across the magnification range. There is quite a lot of chromatic
aberration present on the periphery of the images. This is not so obvious when the images are
resized down to a sane levels.
The working distance is at the lower limits of utility for imaging with reflected light. It is difficult to get
light on the subject when the front of the lens is between 4 mm and 7mm from the object. A typical 20x
objective will have a working distance of about 3 mm - not enough for good lighting with reflected light.
This LWD (Long Working Distance) objective doubles that. There are 20x objectives out there that
provide even more working distance. These are generally called SLWD (Super LWD) and ELWD
(Extra LWD).
When compared to other lenses in its magnification range, 12 mm bellows lenses, this lens
out-resolves all of them. The only specification that it compares unfavorably with a 12 mm bellows lens
is in the chromatic aberration numbers and the color fringing is not so obvious with real-world image
sizes. They tend to have comparable or minimally better working distance than this objective.
Basic Function: Requires extension tubes or bellows to focus.
Appearance:
Aperture: fixed aperture.
Image Samples:
About 20:1 magnification, focus stack of 128 images, resized: This image is the point of a star on a morgan dollar.
About 20:1 magnification, 1 to 1 crop of a source
image from above:
Good pixel level detail for the magnification. You just
can't expect things to be sharp at this level of
magnification. Each pixel on the image to the right is
about 0.3 micrometers.
You can see a little purple fringing on the edge of the
star on the above image. This aberration is thought to
be related to the microlenses in front of each pixel on
the detector. It is not chromatic aberration associated
with the lens. It can be decreased by softening of the
lighting.
image from above:
Good pixel level detail for the magnification. You just
can't expect things to be sharp at this level of
magnification. Each pixel on the image to the right is
about 0.3 micrometers.
You can see a little purple fringing on the edge of the
star on the above image. This aberration is thought to
be related to the microlenses in front of each pixel on
the detector. It is not chromatic aberration associated
with the lens. It can be decreased by softening of the
lighting.
Distortion: There is no obvious distortion visible with this lens.
Performance: Sharpness vs Magnification:
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit into the hierarchy that I
have created.
The Nikon 20/0.4 LWD shows very good
sharpness performance across its magnification
range.
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit into the hierarchy that I
have created.
The Nikon 20/0.4 LWD shows very good
sharpness performance across its magnification
range.
Performance: Resolution vs Magnification:
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit into the hierarchy that I
have created.
The Nikon 20/0.4 LWD shows a strong very good
resolution performance across its magnification
range.
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit into the hierarchy that I
have created.
The Nikon 20/0.4 LWD shows a strong very good
resolution performance across its magnification
range.
